My husband tried to put in a Lynksys wireless card into our desktop....with out reading and following instructions....and now the monitor will not work with desktop...but it does work with another desktop...does anybody know what he might have done to the desktop..?

do you have a video card installed on the computer? if so, double check to make sure that the monitor is plugged into the video card and not the onboard video. (It will be the lower one that you're looking for). check that, and let me know how you make out. it's a common mistake people make.

In addition, was the computer case opened when you installed the wireless card? If so, make sure that other cards are seated properly.

When you power the computer on, do you hear the fans spin, hard drive spin up?

Ifthe monitoe is not working check your signal cable which is backwarsds may be its a problem with that

The problem you are facing is not associated with the wireless card or like that. The problem is associated with Monitor or video card for the system. As you have mentioned it is working fine with another desktop, then the problem might be associated with the monitor only.